1. Field of the Invention
The present invention relates to an ink composition, an ink set, and an image forming method.
2. Description of the Related Art
Ink jet techniques allow intended image formation on a variety of recording media, and therefore are an image recording method widely promising in the field of office and home printers, as well as in the commercial field.
As ink used for ink jet recording, besides solvent-based ink, water-based ink is drawing attention from a viewpoint of considering global environment and work environment. Particularly, a technique for forming images exhibiting high rub fastness, such as resistant to scratches by curing a water-based pigment ink composition containing a polymerizable monomer component has been under investigation.
As one of such techniques for forming images, for example, an inkjet recording method has been disclosed (see, for example, Japanese Patent No. 3,642,152) in which printing is performed on a recording medium by depositing an ink composition containing an acrylate monomer and/or a resin emulsion and a reaction liquid containing a photopolymerization initiator and a reactive agent that produces aggregate in contact with the ink composition. Further, an ink of one-component type used for inkjet recording has been disclosed (see, for example, Japanese Patent No. 3,576,862) which includes a specific cationic oligomer and a photopolymerization initiator, together with a colorant and water.
Meanwhile, there are a variety of compounds currently known as initiators initiating the polymerization of polymerizable monomers. Those compounds can be appropriately selected based on needs and purposes. However, there are cases where solubility of the initiator in water-based solvents cannot necessarily be satisfactory.
The conventional techniques use a photopolymerization initiator in water-based pigment ink, in which, however, no consideration is given to the initiator solubility. Thus, when satisfactory initiator solubility is not obtained, ink stability is deteriorated and also images cannot have sufficient rub fastness. In addition, when image surfaces are in contact with each other over time, the images may partially adhere to each other and may not be able to be separated. When the ink is aged under a low temperature condition, this becomes conspicuous. Such ink is also not suitable for high-speed recording.
Furthermore, the method described in Patent Literature 1, which is a technique for immobilizing ink by reaction of a reaction solution with an ink, is also insufficient in terms of immobilization of images.
The present invention has been accomplished in view of the above circumstances. It is an object of the present invention to provide both an ink composition and an ink set that exhibit high temporal stability under various temperature conditions including a low temperature and allow to form images with favorable rub fastness, and to provide an image forming method for forming images with high rub fastness.